[PATCH 07/19] powerpc: Create mtmsrd_isync()

[Michael Ellerman]

On Tue, 2015-12-01 at 22:23 +1100, Michael Ellerman wrote:

> On Thu, 2015-10-29 at 11:43 +1100, Anton Blanchard wrote:
> 

> > mtmsrd_isync() will do an mtmsrd followed by an isync on older
> > processors. On newer processors we avoid the isync via a feature fixup.
> > 
> > diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
> > index ef64219..5bf8ec2 100644
> > --- a/arch/powerpc/kernel/process.c
> > +++ b/arch/powerpc/kernel/process.c
> > @@ -130,7 +130,10 @@ void enable_kernel_fp(void)
> >  		check_if_tm_restore_required(current);
> >  		giveup_fpu(current);
> >  	} else {
> > -		giveup_fpu(NULL);	/* just enables FP for kernel */
> > +		u64 oldmsr = mfmsr();
> > +
> > +		if (!(oldmsr & MSR_FP))
> > +			mtmsr_isync(oldmsr | MSR_FP);
> 
> You seem to do this pattern at all call sites.
> 
> So should we instead have a helper that makes sure an MSR bit(s) is/are set?
> 
> Maybe:
> 
> static inline void msr_enable(unsigned long enable_bits)
> {
> 	u64 val, msr = mfmsr();
> 
> 	if (msr & enable_bits)
> 		return;
> 
> 	val = msr | enable_bits;
> 	asm volatile(__MTMSR " %0; " ASM_FTR_IFCLR("isync", "nop", %1) : :
> 			"r" (val), "i" (CPU_FTR_ARCH_206) : "memory");
> }

Ugh, should have read the whole series. You do more or less this in patch 12.

cheers